setup questions

Hi,

This is my 3rd posting, some questions here. Previously my post was purely on split dns using LAN IP's. But now my boss want to use Public IP to utilise the Zimbra Open Source server, and it isn't natted.

The situation is :

1. I have domains hosted at Plesk Control in Data Center, and properly setup the DNS,MX and A records.
2. I have a runnning server using ZCS using split dns methods in LAN mode, thanks to this forum and kind helps from Zimbra guru's here.

The question is :
1. I want to use Public IP address to setup Zimbra Open Source server, which isn't natted. Can i use the Public IP without using split dns setup? If can, what should i do, do i need to follow some of the steps briefed in Split Dns, such as creating .db files, hosts files and resolv.conf file?

2. I also want to add a few domains after i have setup the ZCS using Public IP address, maybe in the future. Is it each time i want to add domains, i need to do some modifications on the zimbra files, such as, named.conf, db or zone files?

3. Do i need to setup PTR in the zimbra file setup, to receive and send emails properly, such as in Yahoo, Gmail or Hotmail ? If yes, where should i add the PTR records in zimbra configuration ?

4. Can i move the Public IP address into natted environment, let say in the near future,, without affecting the server performance? And when doing that, do i need to setup any zimbra configuration files again ?

These are the questions that i need some briefing so that i can proceed with the above said planning. Hope the guru's here can clear some of my doubts here.